Late spring and summer patterns of euphausiid reproduction in Southeast Alaska fjord waters

Abstract

Abundance, size and developmental stage data for furcilia and juvenile euphausiids together with data on the timing and prevalence of attached spermatophores on adult females are used to infer times of spawning by 4 euphausiid species in Frederick Sound and lower Stephens Passage, Southeast Alaska. Results from net tows conducted between late May and September 2008 and a single, opportunistic dip-net sample on 21 April indicate that Thysanoessa raschii and T. longipes spawned in association with the spring phytoplankton bloom in April and continued spawning until June, with juveniles first appearing in mid-to late June. Presence of female T. spinifera carrying spermatophores in mid-April indicates that T. spinifera spawns in association with the spring bloom as well; however, absence of larval T. spinifera suggest that spawning in the inshore waters is comparatively rare. In contrast, observations of female Euphausia pacifica carrying spermatophores from late May to August and the first appearance of early furcilia in August indicate that spawning occurs, at least to some extent, after the primary bloom. However, the appearance of juvenile E. pacifica in late June suggests that spawning occurred earlier as well and in discrete bouts. We argue that the absence of E. pacifica furcilia that were likely to have originated from an early spawning event may indicate that E. pacifica juveniles observed in late June were advected into the study region from the Gulf of Alaska. Overall, phenology of seasonal reproduction in this Alaskan fjord is similar to that observed in coastal waters in arctic and temperate ecosystems.

Fluctuating reproductive rates in Hawaii's humpback whales, Megaptera novaeangliae , reflect recent climate anomalies in the North Pacific

“…In Alaska waters, humpback whale prey preferences vary seasonally and regionally [84,88–91]. During the summer months in Southeast Alaska, mature euphausiids ( Thysanoessa sp., Euphausia pacifica ) are a preferred prey in some regions [88,92], while in other areas, such as Icy Strait and Glacier Bay, primary prey targets include small schooling fish such as capelin ( Mallotus villosus ), juvenile wall-eye pollock ( Gadus chalcogrammus ) and Pacific herring ( Clupea pallasii ). During fall, targeted prey vary regionally between herring and euphausiids.…”

Examining the Role of Marine Mammals and Seabirds in Southeast Alaska’s Marine Ecosystem Dynamics

“…Zooplankton includes a variety of taxa that includes euphausiids, copepods, and larval fish. Primary production in the area is known to have a positive impact on euphausiid reproduction with spawning periods overlapping with the spring phytoplankton bloom (Szabo and Batchelder, 2014). Zooplankton is the primary prey item for the majority of the model variables but relatively little research has been done in the region to examine detailed species compositions.…”

“…Zooplankton is the primary prey item for the majority of the model variables but relatively little research has been done in the region to examine detailed species compositions. However, Szabo and Batchelder (2014) reported the presence of four euphausiid species (Thysanoessa raschii, T. longipes, T. spinifera, and Euphausia pacifica) in Frederick Sound and lower Stephens Passage during the late spring and summer. Overall, zooplankton is a key prey item for juvenile salmon, forage fish, juvenile piscivorous fish, and humpback whales (Dolphin, 1987;Burrows et al, 2016;Zador et al, 2019;Fergusson et al, 2020).…”